Genetic engineering of forest tree species to conform to desired traits has shifted the emphasis in forest tree improvement away from the traditional breeding programs during the past decade. Although research on genetic engineering of forest trees has been vigorous, the progress has been slow due.
The ability to make trees grow faster and be disease resistant to produce the highest volume of wood in the shortest period of time has been and continues to be the top objective of many forest products company worldwide. The ability to genetically increase the optimal growth of trees would be a commercially significant improvement. Faster growing trees could be used by all sectors of the forest and wood products industry worldwide.
Lignin, a complex phenolic polymer, is a major component in cell walls of secondary xylem. In general, lignin constitutes 25% of the dry weight of the wood, making it the second most abundant organic compound on earth after cellulose. Although lignin plays an important role in plants, it usually represents an obstacle to utilizing biomass in several applications. For example, in woodpulp production, lignin has to be removed through expensive and polluting processes in order to recover cellulose.
Thus, it is desirable to genetically engineer plants with reduced lignin content and/or altered lignin composition that can be utilized more efficiently. Trees that could be genetically engineered with a reduced amount of lignin would be commercially valuable. These genetically engineered trees would be less expensive to pulp because, in essence, part of the pulping has already been performed due to the reduced amount of lignin.
Trees with increased cellulose content would also be commercially valuable to the pulp and paper industry.
Disease resistance in plants is also a most desirable plant trait. The impact of disease resistance in trees on the economy of forest products industry worldwide is significant.
Promoters that target specific plant tissue could be useful in manipulating gene expression to enable the engineering of traits of interest in specific tissue of plants, such as, xylem and epidermal tissues.
Although studies have revealed several general properties of plant p-coumarate Co-enzyme A ligase (CCL), the role of CCL in regulating the synthesis of monolignols in response to different states of development and environmental stress in tree species remains largely unknown. Furthermore, multiple CCL isoforms are normally present in plants, channeling phenolic compounds to the biosynthesis of not only lignin but also other phenylpropanoids, such as flavonoids. Since CCL isoforms have not been previously cloned from tree species for the identification of their biochemical functions, the presence of CCL isoforms remains so far as a challenge to a specific control of metabolic flux to the lignin biosynthesis in tree species.